Liquid propellant containing chromium coated beryllium powder dispersed therethrough

ABSTRACT

THIS INVENTION RELATES TO IMPROVEMENTS IN LIQUID PROPELLANTS. AN OBJECT OF THE PRESENT INVENTION IS TO PROVIDE A LIQUID PROPELLANT CONTAINING BERYLLIUM AND WHEREIN THE BERYLLIUM IS SURFACE TREATED WITH A CHROMIUM CONTAINING COATING SO AS TO RENDER THE SAME LESS REACTIVE TO ITS ENVIRONMENT.

United States Patent 3,586,550 LIQUID PROPELLANT CONTAINING CHROMIUM COATED BERYLLIUM POWDER DISPERSED THERETHROUGH Simon J. Morana, Hazleton, Pa., assignor to Kaweckl Berylco Industries, Inc. No Drawing. Filed Mar. 26, 1965, Sen No. 443,161 Int. Cl. C06b 15/00 US. Cl. 149-1 Claims ABSTRACT OF THE DISCLOSURE This invention relates to improvements in liquid propellants. An object of the present invention is to provide a liquid propellant containing beryllium and wherein the beryllium is surface treated with a chromium containing coating so as to render the same less reactive to its environment.

Another object of the invention is to provide a liquid propellant containing beryllium and having improved physical properties and wherein the propellant formulation is not subject to objectionable gassing or explosion.

More specifically an object of the invention is to provide a liquid propellant of the character stated in the preceding paragraphs in which the metal powder of the mixture is in a passive state.

Still more specifically, an object of the invention is to provide a liquid propellant comprising a gel formulation comprising a gelling agent, surface treated beryllium powder, and anhydrous hydrazine and wherein the beryllium powder is surface treated to render the same relatively inert to its environment.

The surface treatment of beryllium powder in accordance with the present invention and as hereinafter described, results in rendering the powder less reactive to its environment with the further result that a more readily controlled propellant composition is obtained.

Liquid propellants containing metal powders are generally in the form of gels or slurries. The use of beryllium metal powders with passivated surfaces had been found to offer definite advantages in liquid propellants over the use of beryllium metal powders with untreated surfaces. More specifically, beryllium metal powders whose surfaces are protected with a thin chrome passivation coating film render the beryllium less reactive to its environment.

One high energy gel propellant formulation contains about 25-35% beryllium powder, about .75 gelling agent such as Carbopol (a derivative of polyacrylic acid marketed by B. F. Goodrich Chemical Co.) balance an hydrous hydrazine. Although the exact mechanism for gelling is unknown, it is believed that hydrazonium ions from the hydrazine and carboxyl groups from Carbopol form a reaction to provide the gel structure. There appears to be some chemical reaction taking place between untreated beryllium powder, hydrazine and Carbopol be cause when these three ingredients are mixed in the proper proportions the mixture remains runny and will not gel. Another undesirable feature of this formulation is that the chemical reaction induced by the untreated beryllium powder results in objectionable gassing of the propellant, to the extent that the slurry will swell in size and after several days will actually overflow from the beaker it is contained in.

In order to be useful the gel must not gas, and must have a good storage life from the time it is made to the time it is fired. It has been determined that after applying a thin chrome passivated surface film on the same beryllium metal powder lot used in the above illustration, the mixture using the passivated powder did form a stable gel structure and the gassing problem was eliminated.

3,586,550 Patented June 22,, 1971 Thus, the beryllium metal powder with a passivated chrome film surface behaved more like an inert filler and did not exhibit the side reactions so prominently noticed with the untreated beryllium metal powder.

One procedure for treating the beryllium metal powder comprises subjecting the powder to the action of an aqueous solution mixture of potassium dichromate, Kzcl'zoq, and phosphoric acid, H PO whereby the metal particles pick up, or acquire, a surface coating complex of chromium and phosphorous, and the metal particles become passive or are in a passive state. In the carrying out of the surface treatment procedure hereinabove broadly set forth, a stock solution is made, composed of equal parts by volume of concentrated phosphoric acid and a saturated aqueous solution of potassium dichromate. Different dilutions of the stock solution with water may be employed and will produce desirable surface passivity of the beryllium metal powder.

The activity of the reaction resulting from mixing the stock solution with water decreases as the degree of dilution of the stock solution increases. As an example use may be made of a mixture of equal parts by volume of water in stock solution which gives an active reaction with beryllium powder and dilutions of as much as 50 parts water and 1 part stock solution, while exhibiting a very mild reaction with beryllium powder, gives to the powder very excellent surface passivity.

Using a dilution of 20 parts water to 1 part by volume of stock solution results in a pick up of from .03 to .5% chromium and .01 to .1-0% phosphorus in the surface treated powder, depending on the particle size of the powder.

Another stock solution employed for effecting the desired surface treatment consists of a saturated aqueous solution of potassium dichromate which when diluted with not more than 5 parts by volume of water results in excellent surface treatment passivity. Using a 1 to l dilution of this solution with water results in a chromium pick up from .2 to .9%.

While it is not clearly understood what exact mechanism is involved in connection with the surface treatment which results in the passivity of the metal particles, X-ray diffraction studies indicate that the surface treated powders contains less beryllium oxide than the untreated beryllium powders.

While the chromium coating received by the powder particle may be of varying thicknesses, it has been calculated that a monomolecular coating of chromium on the surface of a 4 micron particle size beryllium metal sphere would result in .lOl% chromium.

As a more specific illustration of the process of the invention, the following example is given:

5 gallons of surface coating solution consisting of 1 pint of reagent grade to phosphoric acid, 1 pint of saturated solution of potassium dichromate and 4% gallons of water, cooled to room temperature, was placed in a stainless steel vessel, fitted with an agitator. 6 pounds of nominal 10 micron beryllium subsieve powder was gradually added over a period of 10 minutes, with agitation, and the agitation was continued an additional 20 minutes.

The slurry was filtered and the filter cake was washed with 5 gallons of water and refiltered, and the resulting filter cake was dried under vacuum to produce the surface treated powder.

The solution of the foregoing example gives a dilution of the acid-dichromate mixture of about 1 to 19. The reaction with the beryllium powder is relatively mild and gives a surface coated powder having excellent passivity.

Another chromium containing solution may be employed, made up from the stock solution consisting of chromium anhydride, CrO and phosphoric acid.

A saturated solution of the chromium anhydride is mixed with an equal volume of concentrated phosphoric acid to make the stock solution. A dilution of 1 part of this stock solution with 20 parts of water, used for treating the beryllium metal powder gives powdered particles having excellent surface passivity.

A surface treated beryllium powder is mixed with the gelling agent and the anhydrous hydrazine and the mix ture formed a stable gel structure with no gassing.

Another type of liquid propellant involves the use of beryllium metal powder slurried or gelled with liquid oxygen in a cryogenic system. To determine the relative reactivity of beryllium metal powder with liquid oxygen, approximately 50 ml. of liquid oxygen is placed in a wide mouth pint glass insulated model, and 10 grams of beryllium metal powder was poured onto the liquid oxygen. This procedure was repeated three times with untreated beryllium metal powder and three times with surface passivated beryllium metal powder treated from the same powder lot as the untreated berryllium metal powder in order to eliminate variables, such as particle size and chemistry of the beryllium metal powder. In each test with the untreated beryllium metal powder, there was an explosion of such a nature that the glass insert was shattered to pieces and the outer metal container was distorted out of shape. There was no reaction in each of the three tests using beryllium powder with the thin, chrome film passivated surfaces. This again demonstrates the chemical inertness imparted to beryllium metal powder which has been subjected to the chrome passivation surface coating.

While reference has been made to beryllium subsieve powder, it is to be understood that the invention is applicable to the use of powders of average particle size in the range of from 1 to 100 microns.

All percentages set forth above are by weight of the composition.

I claim:

1. A propellant comprising a liquid propellant selected from the group consisting of gels, slurries and liquid oxygen and having dispersed therethrough beryllium metal powder particles passivated by a chromium containing coating.

2. The composition of claim 1, wherein the liquid propellant is a gel comprising a derivative of polyacrylic acid and anhydrous hydrazine.

3. A propellant as defined in claim 2 wherein the composition comprises about 25-35% beryllium powder, about .75 derivative of polyacrylic acid, with balance anhydrous hydrazine, said percentages being by weight of the composition.

4. A method of inhibiting gassing of liquid propellants of the type consisting of hydrazine, a gel and beryllium powder comprising treating said beryllium powder with a passivating chromium containing coating so as to render the surfaces thereof passive and less reactive.

5. The process of inhibiting the explosive characteristics of a liquid propellant of the beryllium powder liquid oxygen type, comprising providing the beryllium powder with a passivated surface of a chromium containing coating.

References Cited UNITED STATES PATENTS 3,164,505 1/1965 Hsieh et al. 1492 3,228,813 1/1966 Morana 149-5 3,232,801 2/1966 BOst et a1. 149-36 CARL D. QUARFORTH, Primary Examiner I. J. LECHERT JR., Assistant Examiner US. Cl. X.R. 

